The uniformity of the WFC and HRC detector response has been assessed
using multiple dithered pointings of 47 Tucanae. By placing the same
stars over different portions of the detector and measuring relative
changes in brightness, low frequency spatial variations in the
response of each detector have been measured. The original WFC and HRC
laboratory flat fields produce photometric errors of 5 to 18 percent
from corner-to-corner. The required low-order correction (L-flat) has
been applied to the lab flats, and new flat fields have been delivered
for use in the calibration pipeline. Initial results suggest the
photometric response for a given star is now the same to ~1 for any
position in the field of view. As a further test, the improved flat
fields are compared with observations of the bright earth at UV
wavelengths (F330W) and with skyflats from ERO data at long
wavelengths (F775W).
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Last modified November 29, 2002.
Roeland van der Marel,
marel@stsci.edu.
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